146 BOTANICAL GAZETTE [SEPTEMBER 
recapitulation of its ancestral development (phylogenesis). A 
critical study of the development of the individual must throw 
light upon the past history of the species. When we know 
every step in the formation of each plant we shall be able to 
trace the phylogeny of every species. Here again we have to 
face the fact that our knowledge is still quite fragmentary, and 
that on this account the results are not as definite as we could 
wish. And yet, when we bring together what we know of the 
ontogeny of plants here and there in the higher groups, we are 
able to make out with much certainty not a little as to their 
phylogeny. To the details regarding these results I shall advert 
somewhat later. 
There is still another line of inquiry open to us, namely, the 
morphological, in which account is taken of the varying develop- 
ment of homologous tissues, members, and organs. Rightly 
interpreted, the results of morphological studies are of very 
high importance in determining genetic relationships. When 
differences in homologous parts are regarded as but the expres- 
sion of variation from a common form, they become indices of 
relationship, and when these indices, obtained from all the tis- 
sues, members, and organs of a group of plants, are judiciously 
considered, they mark out lines of descent with great dis- 
tinctness. 
We have thus open to us three lines of investigation in the 
study of the phylogeny of plants, namely, (1) the historical, in 
which the materials are supplied by phytopalzontology, (2) the 
ontogenetic, in which the development of the individual supplies 
us with the necessary data, and (3) the morphological, in which 
the different development of homologous parts is our index of 
relationship. In this paper I purpose to bring these three lines 
of investigation to bear upon the problem of the phylogeny | of 
the angiosperms. 
GENERAL RESULTS FROM PHYTOPALAONTOLOGY. 
In the Devonian period plants underwent such modifications 
that we pretty cleatty *rcte eas (Ge re guards which oo : 
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